1. Field of the Invention
This invention relates to a method of coloring a polycarbonate extruded or molded product for optical members such as an optical disk, an optical card, an optical waveguide and an optical fiber. More particularly, it relates to a method of coloring a polycarbonate extruded or molded product for optical members, which is colored by a liquid coloring process for obtaining a colored polycarbonate extruded or molded product for optical members in an extruder or injection molding machine.
2. Description of the Prior Art
In recent years, various optical members are often manufactured in the form of extruded or molded products using organic polymeric materials. Such optical members include optical reproduction-only digital audio disks as exemplified by CD, CD-V and CDROM, or optical reproduction-only analog video disks as exemplified by LD, as well as other optical disks, optical cards, optical waveguides, optical fibers, and other optical members.
Incidentally, an acrylic resin (PMMA) used when substrates for optical disks are formed has the features that it facilitates the control of molecular configuration to make it hard to produce double diffraction, has good transfer properties because of its high fluidity, can decrease the residual strain of an extruded or molded product, and also has no serious problems in thermal resistance, surface hardness, mechanical properties, solvent resistance, transparency, durability, etc. It, however, has the disadvantage that two sheets must be laminated when used, because of a great warpage that may be caused by absorption of moisture. A polycarbonate resin has the features that it has a superior moisture absorption, has good mechanical properties and thermal resistance, has a superior dimensional stability, and promises a high reliability for a long period of time, but on the other hand has the problems that it tends to produce double diffraction because of its molecular structure, and must be extruded or molded at a high temperature because of its poor fluidity. As a polycarbonate resin for optical members, however, a resin has been provided whose molecular weight is decreased to improve the fluidity. It has now become usual to prepare optical cards, optical waveguides, optical fibers and other optical members by the use of such a resin.
An optical member obtained in the form of an extruded or molded product using the polycarbonate resin for optical members has been hitherto prepared in the form of a product to which no coloring agent (dye and/or pigment) is added do that the optical member can make the most of its transparency. In recent years, however, there is a demand for the advent of an optical member comprised of an extruded or molded product of a polycarbonate resin for optical members which has been colored with a coloring agent, for the purposes of improving decorativeness or imparting selectivity to wavelengths.
Referring to a method of obtaining an extruded or molded product of a colored polycarbonate resin for optical members, various conventional processes for preparing extruded or molded products of colored synthetic resins can be considered utilizable, including 1) the colored-material process in which a mixture comprised of a powdery coloring agent (dye and/or pigment) and a synthetic resin powder is melt-extruded to give pellets of synthetic resin colored with a coloring agent (dye and/or pigment), and an extruded or molded product of a synthetic resin is formed by an extruder or an injection molding machine by the use of the synthetic resin thus colored, 2) the master batch process in which an extruded or molded product of a synthetic resin is formed by an extruder or an injection molding mechine by the use of a mixture comprised of a master pellet of a synthetic resin containing a coloring agent (dye and/or pigment) in a high concentration, and a pellet of an uncolored synthetic resin, 3) the dry coloring process in which an extruded or molded product of a synthetic resin is formed by an extruder or an injection molding machine by the use of a mixture comprised of a synthetic resin pellet and a powdery coloring agent (dye and/or pigment), and 4) the liquid coloring process in which, in an extruder or an injection molding machine used for extruding or molding a synthetic resin, a synthetic resin and a liquid coloring agent dispersion obtained by dispersing a coloring agent in a dispersing agent are mixed, and thereafter the both are melted so that an extruded or molded product of a colored synthetic resin can be obtained.
Of the processes 1) to 4) having been conventionally used when extruded or molded products of colored synthetic resins are prepared, the process 1) colored-material process is a process in which colored synthetic resin pellets are used. Hence, this process requires material feed tanks that separately hold pellets of synthetic resins separately colored for each kind of required colors, and pipes that separately feed materials in a solid state from the individual material feed tanks to an extruder or an injection molding machine. This results in a large scale of equipment. In addition, the colored synthetic resin pellets are expensive and consequently extruded or molded products can not be produced at a low cost when they are produced in varieties is small quantities. The process 2) master batch process can be carried out using simple equipment, compared with the above process 1) colored-material process. Also in this process, however, extruded or molded products can not be produced at a low cost when they are produced in varieties in small quantities. The process 3) dry coloring process has the problem that dust tends to be included in the course of processing. The method 4) liquid coloring process requires no pellets of specially colored synthetic resin. It also makes it possible to feed using simple equipment a liquid coloring agent dispersion obtained by dispersing a coloring agent in a dispersing agent, to an extruder or an injection molding machine for extruding or molding synthetic resins. It further makes it easy to construct an apparatus in the manner that no dust may be included in the course of extrusion or molding. Thus, this process has no problems that are involved in the above processes 1) to 3), and can provide extruded or molded products at a low cost when they are produced in varieties in small quantities.
In the instance where a polycarbonate extruded or molded product for optical members is colored according to the above process 4) liquid coloring process, what has been conventionally used is a liquid coloring agent dispersion obtained by dispersing a coloring agent (dye and/or pigment) in a dispersing agent of a paraffin type, a dispersing agent of the type of a fatty acid ester of an oxyalkylene, or a dispersing agent of an unsaturated fatty acid ester type. Since, however, these various dispersing agents have a poor compatibility with a polycarbonate resin for optical members, this has caused the problem that no polycarbonate extruded or molded product for optical members which has good optical characteristics can be obtained because of occurrence of microscopically detectable minute changes in shape on the surface of an optical disk, and also has brought about the problem that an optical disk with a high rate of signal errors or a high rate of signal dropout is consequently manufactured particularly when substrates of optical disks such as CD, CD-V and LD are colored by the liquid coloring process.